Okay, how deep do you wanna go here? Because this is going to be a TL;DR...
Fixed costs can be a bitch when business is slow, but they are an even bigger bitch when the doors are locked, so for most restaurants, opening at limited capacity is going to be very attractive, since they will probably expect to lose less money than they are losing right now. However, different groups of restaurants are operating on different models right now, and they will view this type of reopening differently. I can think of three distinct groups, from worst-positioned to best:
First are the restaurants who cannot manage their fixed costs even closed. For the most part, we are talking about restaurants that are carrying a lot of debt, so even if they lay off the entire management team, they don't have enough in savings to keep the electricity running (gotta keep that freezer on!), pay the rent, or make loan payments. These restaurants have deadlines by which they need business to get back to pre-Covid levels or they close. Some have already closed. Others will be closing soon. A limited opening might allow some of them to stretch the pain out a little longer, but they can all see the end.
Second are the restaurants who were able to manage their fixed costs by closing. These are generally going to be restaurants that furloughed most of their management teams (and support teams in the case of large companies), don't carry a lot of debt, and have enough cash reserves to keep paying the rent and bare necessities even while the doors are locked. They are probably very iffy about a soft open. On the one hand, they are already losing money, so maybe some revenue could help, but on the other hand, opening is going to bring some extra fixed costs back into play (more salaries, insurance, etc.), so there is a minimum level of sales they will need to do to make it at least as good as staying closed.
Third are the restaurants who aren't closed right now. The ones who have gone to a carryout-only model have found a way to make it work. Most of them are only surviving right now, not thriving, but their fixed costs are just as high as they ever were before (or close, at any rate). For them, a soft open carries many of the risks of the second group above, but they have an added advantage: they are expecting the recent increase in carryout business to continue, perhaps not at the current level, but certainly at a level much higher than pre-Covid times. For these restaurants, sales will be down from last year, but not nearly as much as one might expect, since a big chunk of those sales have simply moved off-site. Expectations at 25% capacity may be that sales are somewhere in the range of 40-70% of what they were the previous year, which isn't great, but can be done profitably.
Long story short, for most restaurants and restaurant groups (at least the well-managed ones), fixed costs aren't the problem. Restaurants tend to have higher labor and higher product cost than most other retail industries, so it will be easier for restaurants to handle the scaling down of costs that will be necessary. For the restaurants that are bleeding from fixed costs, as I mentioned above, they are all screwed, anyway.